Title |
Effects of rehydration on physiological and transcriptional responses of a water-stressed rhizobium |
Author |
Jie Zhu1,2, Xin Jiang1,3*, Dawei Guan1, Yaowei Kang4, Li Li3, Fengming Cao1,3, Baisuo Zhao3, Mingchao Ma1,3, Ji Zhao2, and Jun Li1,3* |
Address |
1Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, P. R. China, 2School of Ecology and Environment, Inner Mongolia University, Hohhot 010021, P. R. China, 3Laboratory of Quality & Safety Risk Assessment for Microbial Products (Beijing), Ministry of Agriculture, Beijing 100081, P. R. China , 4Life Sciences College of Zhaoqing University, Zhaoqing 526061, P. R. China |
Bibliography |
Journal of Microbiology, 60(1),31-46, 2022,
|
DOI |
10.1007/s12275-022-1325-7
|
Key Words |
Bradyrhizobium japonicum, symbiotic nitrogen
fixation, water stress, dilution, gene expression |
Abstract |
As a microsymbiont of soybean, Bradyrhizobium japonicum
plays an important role in symbiotic nitrogen fixation and
sustainable agriculture. However, the survival of B. japonicum
cells under water-deplete (e.g., drought) and water-replete
(e.g., flood) conditions is a major concern affecting their
nitrogen-fixing ability by establishing the symbiotic relationship
with the host. In this study, we isolated a water stress tolerant
rhizobium from soybean root nodules and tested its
survival under water-deplete conditions. The rhizobium was
identified as Bradyrhizobium japonicum and named strain
5038. Interestingly, both plate counting and live/dead fluorescence
staining assays indicate that a number of viable but
non-culturable cells exist in the culture medium upon the rehydration
process which could cause dilution stress. Bradyrhizobium
japonicum 5038 cells increased production of exopolysaccharide
(EPS) and trehalose when dehydrated, suggesting
that protective responses were stimulated. As expected,
cells reduced their production upon the subsequent rehydration.
To examine differential gene expression of B. japonicum
5038 when exposed to water-deplete and subsequent waterreplete
conditions, whole-genome transcriptional analysis was
performed under 10% relative humidity (RH), and subsequent
100% RH, respectively. A total of 462 differentially expressed
genes (DEGs, > 2.0-fold) were identified under the 10% RH
condition, while 3,776 genes showed differential expression
during the subsequent rehydration (100% RH) process. Genes
involved in signal transduction, inorganic ion transport, energy
production and metabolisms of carbohydrates, amino
acids, and lipids were far more up-regulated than downregulated
in the 10% RH condition. Notably, trehalose biosynthetic
genes (otsAB, treS, and treYZ), genes ligD, oprB, and
a sigma factor rpoH were significantly induced by 10% RH.
Under the subsequent 100% RH condition, genes involved in
transcription, translation, cell membrane regulation, replication
and repair, and protein processing were highly up-regulated.
Interestingly, most of 10%-RH inducible genes displayed
rehydration-repressed, except three genes encoding heat shock
(Hsp20) proteins. Therefore, this study provides molecular
evidence for the switch of gene expression of B. japonicum
cells when encountered the opposite water availability from
water-deplete to water-replete conditions. |